I agree about every bbl being unique.
I doubt it would be anywhere near 150 fps. total tho.
See "Fastest 338 without Cheytac" thread, Last pg. Post #29 by Kirby Allen (fiftydriver) in this section, page 3.
Im guessing somewhere in the 20-40 fps per inch with the RUM. I could be WAAAAAY off here, but if I'm interpreting Kirbys results correctly, I'd say you'll gain some for sure, but not any massive amount. Maybe I'm underestimating a bit, maybe not, but I'd rather figure low, & be pleasantly suprised with any extra.
I used to go with the 50-60 fps per inch theory, but looking at the link, & the post Kirby wrote, I don't know that it even aplies at all anymore.

For me it's been no contest, 338 RUM!!! I've gone through the 7mm, 300 and 338 RUM in some variations and with the 338 your getting something for your powder and barrel!! With your 300 RUM your only getting 140 ft lbs of energy more at 1000yrds than I do with my 270 WSM loaded with a 175 gr Matrix and I use only 64 gr of Retumbo.

I agree about every bbl being unique.
I doubt it would be anywhere near 150 fps. total tho.
See "Fastest 338 without Cheytac" thread, Last pg. Post #29 by Kirby Allen (fiftydriver) in this section, page 3.
Im guessing somewhere in the 20-40 fps per inch with the RUM. I could be WAAAAAY off here, but if I'm interpreting Kirbys results correctly, I'd say you'll gain some for sure, but not any massive amount. Maybe I'm underestimating a bit, maybe not, but I'd rather figure low, & be pleasantly suprised with any extra.
I used to go with the 50-60 fps per inch theory, but looking at the link, & the post Kirby wrote, I don't know that it even aplies at all anymore.

The rule of thumb is 50-100fps, but I think it's more like 30-75fps which is why I went with the possible spread I did.

Quality of the barrel and chambering makes a big difference as does the powder being used.

Like most things we discuss here there are a hell of a lot of factors involved.

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A 1-10 will stabilize a 210 nicely, Berger lists the 230gr OTM for a 1-10 twist as well. If I ever went back to the 30 cals it would be to shoot the upper level of weights where you can get more for the bang but your still going to have the possibility of eating barrels.